The proposed research focuses on the mechanism of virus infection, especially on the functional interaction of virus particle and host cell surface. Two steps are recognizable before infection occurs: 1) collision of virus and host cell with subsequent attachment; 2) the virus DNA release leading to infection of the cell. To study both steps, different methods had to be developed; virus-cell collisions were determined by a) absorption kinetics, b) mathematical modeling (computer simulation), and c) fluorescence depolarization, a method still to be further advanced for the required resolution. The adsorption step is not immediately followed by infection; instead, a time-span elapses of characteristic length for each virus type. We found recently (for one virion type) that the virus attachment, DNA ejection, and the cell membrane de-energization follow each other very rapidly. We will measure the membrane changes by fluorescence of voltage sensitive dyes. We propose to study the fast infection processes in a greater variety of bacterial viruses, in order to characterize 1) the membrane signal which causes nucleic acid release of the virus, and 2) the functional inhibition at the injection step employing biochemical and biophysical manipulation of the membrane.